The present invention relates to optical modulation apparatuses and, more specifically, to an optical modulation apparatus that uses a light source and a device for ON/OFF control of light outputted from the light source.
In one conventional optical modulation apparatus that uses a light source and a device for ON/OFF control of light outputted from the light source, by controlling the device for ON/OFF control of the output light to vary the density of ON time (typically, by carrying out pulse-width modulation or pulse-number modulation), light is outputted that has luminance according to a provided luminance signal. At this time, the apparatus is structured to operate by varying density during ON time in a unit of a clock signal (that is, to modulate the pulse width or pulse number of the output light from the light source within a unit of the clock signal).
Described below is the conventional optical modulation apparatus with reference to drawings.
FIG. 20 is a block diagram showing the structure of the conventional optical modulation apparatus. In FIG. 20, the conventional optical modulation apparatus includes a pulse-width modulation circuit 101, a power supply.102, a light source 103, and a light valve 104.
The light source 103 is supplied with electric power by the power supply 102 for outputting light. The light valve 104 receives an output pulse (pulse-width modulating signal) from the pulse-width modulation circuit 101 and the output light from the light source 103, and outputs pulse-width modulated light.
FIG. 21 is a block diagram showing one example of structure of the pulse-width modulation circuit 101 of FIG. 20. In FIG. 21, the pulse-width modulation circuit 101 includes a down counter 1011, a flip-flop circuit 1012, and a D flip-flop circuit 1013.
In FIG. 21 when the pulse-width modulation circuit 101 is supplied with a synchronizing signal, the down-counter 1011 loads a value of a signal YS indicating a luminance of a specific pixel according to the synchronizing signal. Simultaneously, the flip-flop circuit 1012 is set to xe2x80x9c1xe2x80x9d.
The value loaded to the down-counter 1011 is down-counted in accordance with a clock signal. When the value becomes 0, the down-counter 1011 outputs a value of 0. This 0 output from the down-counter 1011 resets an output from the flip-flop circuit 1012 to xe2x80x9c0xe2x80x9d. The D flip-flop circuit 1013 takes in the output from the flip-flop circuit 1012 according to the clock signal, and then outputs the same.
If the reset operation has higher priority than any other operation in the flip-flop circuit 1012, when YS is 0, the D flip-flop circuit 1013 does not output any pulse. On the other hand, if YS has a value other than 0, pulses spaced by a time-width in proportion to the value are outputted.
Again in FIG. 20, the pulse-width modulation circuit 101 receives the synchronizing signal, the clock signal, and the YS for carrying out the above operation, thereby outputting pulses spaced by the time-width in proportion to the value of the luminance signal YS. On the other hand, the light source 103 is supplied with electric power by the power supply 102 for outputting light having predetermined intensity. The output light of the light source 103 is supplied to the light valve 104, and ON/OFF-controlled therein with the output pulses from the pulse-width modulation circuit 101.
FIG. 22 is a diagram showing operating waveforms of the conventional optical modulation apparatus (the apparatus of FIG. 20). Shown in FIG. 22 are a waveform indicating output light intensity of the light source 103 and a waveform of the output pulses (pulse-width modulating signal) of the pulse-width modulation circuit 101.
Note that shown in FIG. 22 are the waveforms for four frame periods (from left on the drawing, a first to fourth frame periods; the same goes in the following). One frame period includes eight cycles of the clock signal (that is, one frame period is equal to eight clock periods).
The output light of the light source 103 having the intensity waveform as shown in FIG. 22 and the output pluses (pulse-width modulating signal) of the pulse-width modulation circuit 101 having the waveform as shown in FIG. 22 are supplied to the light valve 104. From the light valve 104, light having the luminance xe2x80x9c8xe2x80x9d at maximum is outputted. This light has the luminance xe2x80x9c8xe2x80x9d during the first field period, the luminance xe2x80x9c4xe2x80x9d during the second field period, the luminance xe2x80x9c2xe2x80x9d during the third field period, and the luminance xe2x80x9c1xe2x80x9d during the fourth field period.
The luminance described herein is a value obtained by time-integrating the output light intensity of the light source 103 over one frame period. In the example of FIG. 22, the output light intensity of the light source is constant (=1), and the luminance of the light outputted from the light valve 104 is represented by a density, per one frame period (=eight clock periods), representing the number of clock periods during which the light valve 104 is ON.
Therefore, if the light valve 104 is OFF during one frame period, the output light luminance of the light valve 104 during that frame period is xe2x80x9c0xe2x80x9d.
Also, if the light valve 104 is ON at the density of one clock period per one frame period, the output light luminance is xe2x80x9c1xe2x80x9d, and this is minimum luminance for the light (that is, the darkest) outputted from the light valve 104 (the fourth frame). Similarly, the output light intensity for ONs for eight clock periods is xe2x80x9c8xe2x80x9d, and this is maximum luminance for the light (that is, the brightest) (the first frame).
In other words, the optical modulation apparatus of FIG. can output light of nine types of luminance including xe2x80x9c0xe2x80x9d.
Note that description has been made in the foregoing for a case where the light valve 104 has only one pixel. In this case, there needs only one pulse-width modulation circuit 101. However, there exists a light valve having a plurality of pixels as shown in FIG. 23, and an optical modulation apparatus using such light valve has been made for practical use.
FIG. 23 is a diagram showing a light valve having a plurality of pixels and a relation between each pixel of the light valve and a video signal. In FIG. 23, each pixel included in the light valve is supplied with output light from a single light source.
A conventional optical modulation apparatus using the light valve of FIG. 23 includes a plurality of pulse width modulation circuits 101 corresponding to each pixel. Each of the pulse-width modulation circuit 101 is supplied with a value of a luminance signal YS corresponding to each pixel. Then, outputted through the light valve 104 is a ray bundle having a plurality of lights each having a luminance corresponding to each pixel.
As is evident from the above description, in the conventional optical modulation apparatus using the light source 103 and the device (light valve 104) for ON/OFF control of the output light of the light source, for the purpose of increasing the types of luminance (that is, the number of gradations) of light outputted from the light valve 104, it is required to increase the frequency of the clock signal which serves as a unit for ON/OFF control. In other words, the operating speed of the light valve for ON/OFF control of the output light of the light source 103 (that is, the frequency of the clock signal) disadvantageously restricts the number of gradations of the light outputted from the light valve 104.
Therefore, an object of the present invention is to provide an optical modulation apparatus that uses a light source and a device for ON/OFF control of an output light of the light source, the optical modulation apparatus capable of increasing the number of gradations (types of luminance) of light outputted from the device without increasing the frequency of a clock signal which serves as a unit of the ON/Off control of the output light from the light source.
To solve the above problem above, the present invention has the following aspects.
A first aspect of the present invention is directed to an optical modulation apparatus for outputting light having luminance according to a luminance signal. The first aspect comprises light-emitting means for emitting light, and ON/OFF control means for carrying out ON/OFF control of the light from the light-emitting means based on the luminance signal, a synchronizing signal, and a clock signal, and outputting the light having the luminance according to the luminance signal. When a value of the luminance signal is not less than a predetermined value, the light-emitting means emits the light having predetermined intensity, while the ON/OFF control means controls the light from the light-emitting means to become ON at a density according to the luminance signal. When the value of the luminance signal is less than the predetermined value, the ON/OFF control means controls the light from the light-emitting means to become ON at predetermined density, while the light-emitting means emits the light having intensity according to the luminance signal.
In the above first aspect, when the value of the luminance signal is not less than the predetermined value, the light having the predetermined intensity is controlled to become ON at a density (an amount) according to the luminance signal. Otherwise, the light having intensity according to the luminance signal is controlled to become ON at predetermined density (amount). Thus, light having smaller luminance can be outputted without the use of a clock signal of higher frequency (the number of luminance, that is, the number of gradations, is increased). Alternatively, with the use of a clock signal of lower frequency, light having the same luminance can be outputted.
Here, the above predetermined value is typically, as in the following second aspect, a signal value that corresponds to the luminance of light outputted when the ON/OFF control means controls the light outputted from the light-emitting means to become ON at a density of one cycle of the clock signal for one cycle of the synchronizing signal, that is, a signal value that corresponds to minimum luminance that can be generated by the ON/OFF control means that operates by a unit of one cycle of the clock signal.
Moreover, for the purpose of emitting light having intensity according to the luminance signal, as in the following third and fourth aspects, for example, electric power supplied to a light source is controlled based on the luminance signal, or, as in the following fifth and sixth aspects, light from the light source is intensity-modulated based on the luminance signal.
Furthermore, to control the light from the light-emitting means to become ON at predetermined density, pulse-width modulation is carried out as in the following third and fifth aspects, or number-of-pulses modulation is carried out as in the following fourth and sixth aspects, for example.
According to the second aspect, further to the first aspect, the predetermined value is a signal value that corresponds to luminance of the light outputted from ON/OFF control means that is obtained by controlling the light from the light-emitting means to become ON at a density of one cycle of the clock signal for one cycle of the synchronizing signal.
In accordance with the above second aspect, it is possible to output light having smaller luminance than the minimum luminance that can be outputted from the ON/OFF control means. Or, if light having the same minimum luminance is outputted, it is possible to slow the operating speed of the ON/OFF control means.
According to the third aspect, further to the second aspect, the light-emitting means includes a light source, a power supply for supplying electric power to the light source, and a light intensity modulation circuit, supplied with the luminance signal and the synchronizing signal, for generating, based on those signals, an intensity modulating signal, and outputting the intensity modulating signal to the power supply, thereby causing the light source to output light intensity-modulated according to the luminance signal. Further, the ON/OFF control means includes a light valve supplied with light from the light source, and a pulse-width modulation circuit, supplied with the luminance signal, the synchronizing signal, and the clock signal, for generating, based on those signals, a pulse-width modulating signal, and outputting the pulse-width modulating signal to the light valve, thereby causing the light valve to output light modulated in pulse width according to the luminance signal.
In the above third aspect, the intensity modulating signal is generated based on the luminance signal and synchronizing signal, and given to the power supply for supplying electric power to the light source, thereby causing the light source to output light intensity-modulated according to the luminance signal. Also, the pulse-width signal is generated based the luminance signal, the synchronizing signal, and the clock signal, and given to the light valve supplied with the light from the light source, thereby causing the light valve to output pulse-width modulated light according to the luminance signal.
According to the fourth aspect, further to the second aspect, the light-emitting means includes a light source, and a light intensity modulation circuit, supplied with the luminance signal and the synchronizing signal, for generating, based on those signal, an intensity modulating signal, and outputting the intensity modulating signal to the power supply, thereby causing the light source to output light intensity modulated according to the luminance signal. Further, the ON/OFF control means includes a light valve supplied with the light from the light source, and a pulse-number modulation circuit, supplied with the luminance signal, the synchronizing signal, and the clock signal, for generating, based on those signals, a pulse-number modulating signal, and outputting the pulse-number modulating signal to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal.
In the above fourth aspect, the intensity modulating signal is generated based on the luminance signal and the synchronizing signal, and given to the power supply for supplying electric power to the light source, thereby causing the light source to output light intensity-modulated according to the luminance signal. Also, the pulse-number modulating signal is generated based on the luminance signal, the synchronizing signal, and the clock signal, and given to the light valve supplied with the light from the light source, thereby causing the light valve to output pulse-number modulated light according to the luminance signal.
According to the fifth aspect, further to the second aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, a light intensity modulator for intensity-modulating light outputted from the light source, and a light intensity modulator drive circuit, supplied with the luminance signal and the synchronizing signal, for generating, based on those signals, an intensity modulating signal, and outputting the intensity modulating signal to the light intensity modulator, thereby causing the light intensity modulator to output light intensity-modulated according to the luminance signal. Further, the ON/OFF control means includes a light valve supplied with the light from the light intensity modulator, and a pulse-width modulation circuit, supplied with the luminance signal, the synchronizing signal, and the clock signal, for generating, based on those signals, a pulse-width modulating signal, and outputting the pulse-width modulating signal to the light valve, thereby causing the light valve to output light modulated in pulse width according to the luminance signal.
In the above fifth aspect, the intensity modulating signal is generated based on the luminance signal and synchronizing signal, and given to the light intensity modulator for intensity-modulating the light from the light source supplied with predetermined electric power, thereby causing the light intensity modulator to output light intensity-modulated according to the luminance signal. Also, the pulse-width modulating signal is generated based on the luminance signal, the synchronizing signal, and the clock signal, and given to the light valve supplied with the light from the light source, thereby causing the light valve to output pulse-width modulated light according to the luminance signal.
According the sixth aspect, further to the second aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, and a light intensity modulator drive circuit, supplied with the luminance signal and the synchronizing signal, for generating, based on those signals, an intensity modulating signal, and outputting the intensity modulating signal to the light intensity modulator, thereby causing the light intensity modulator to output light intensity-modulated according to the luminance signal. Further, the pulse-width modulation means includes a light valve supplied with the light from the light intensity modulator, and a pulse-number modulation circuit, supplied with the luminance signal, the synchronizing signal, and the clock signal, for generating, based on those signals, a pulse-number modulating signal, and outputting the pulse-number modulating signal to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal.
In the above sixth aspect, the intensity modulating signal is generated based on the luminance signal and the synchronizing signal, and given to the light intensity modulator for intensity-modulating the light from the light source supplied with predetermined electric power, thereby causing the light intensity modulator to output intensity-modulated according to the luminance signal. Also, the pulse-number modulating signal is generated based on the luminance signal, the synchronizing signal, and the clock signal, and given to the light valve supplied with the light from the light source, thereby causing the light valve to output pulse-number modulated light according to the luminance signal.
A seventh aspect is directed to an optical modulation apparatus for outputting light having a luminance according to a luminance signal. The apparatus according to the seventh aspect comprises light-emitting means for emitting light, and ON/OFF control means for carrying out ON/OFF control of the light from the light-emitting means based on the luminance signal for each frame period, a frame synchronizing signal, and a clock signal, and outputting light having luminance according to the luminance signal for each frame period. The light-emitting means emitting the light have each predetermined intensity for each sub-field period. Further, the ON/OFF control means, based on the luminance signal, divides one frame period into a plurality of sub-field periods based on the luminance signal for each frame period, the frame synchronizing signal, and the clock signal, divides one frame period into a plurality of sub-field periods, and generates a sub-field synchronizing signal and a luminance signal for each sub-field period. The ON/OFF control means additionally gives the generated sub-field synchronizing signal to the light-emitting means, and controls, for each sub-field period, the light from the light-emitting means to become ON at a density according to the generated luminance signal for each sub-field period.
In the above seventh aspect, the light having predetermined intensity for each sub-field period is emitted, while the luminance signal for each sub-field period is generated for controlling the light to become ON at a density according to the luminance signal. Thus, light having smaller luminance can be outputted without the use of a clock signal of higher frequency (the number of luminance, that is, the number of gradations, is increased). Alternatively, with the use of a clock signal of lower frequency, light having the same luminance can be outputted. Furthermore, output light from only a single light source can be controlled in density and intensity according to a plurality of luminance signals (corresponding to a plurality of pixels).
Here, for the purpose of emitting light having predetermined intensity for each sub-field period, as in the following eighth and ninth aspects, electric power supplied to a light source is controlled based on the luminance signal, or, as in the following tenth and eleventh aspects, light from the light source is intensity-modulated based on the luminance signal.
Furthermore, to control the light from the light-emitting means to become ON at predetermined density, pulse-width modulation is carried out as in the following eighth and tenth aspects, or pulse-number modulation is carried out as in the following ninth and eleventh aspects, for example.
According to the eighth aspect, further to the seventh aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, and a light intensity modulator drive circuit, supplied with the frame synchronizing signal and the sub-field synchronizing signal, for generating, based on those signals, an intensity modulating signal for each sub-field period, and outputting the intensity modulating signal to the light intensity modulator, thereby causing the light intensity modulator to output light having a predetermined intensity for each sub-field period. Further, the ON/OFF control means includes a light valve supplied with the light from the light intensity modulator, a sub-field drive circuit, supplied with the luminance signal for each the frame period, the frame synchronizing signal, and the clock signal, for generating, based on these signals, the sub-field synchronizing signal and the luminance signal for each the sub-field period, and a pulse-width modulation circuit, supplied with the sub-field synchronizing signal and the luminance signal for each sub-field period, for generating, based on these signals, a pulse-width modulating signal and outputting the pulse-width modulating signal, thereby causing the light valve to output pulse-width modulated light according to the luminance signal for each sub-field period.
In the above eighth aspect, the sub-field synchronizing signal and the luminance signal for each sub-field period are generated based on the luminance signal for each frame period, the frame synchronizing signal, and the clock signal. Then, based on the frame synchronizing signal and the sub-field synchronizing signal, the intensity modulating signal for each sub-field period is generated and outputted to the power supply, thereby causing the light source to output light having predetermined intensity for each sub-field period. On the other hand, the pulse-width modulating signal is generated based on the sub-field synchronizing signal and the luminance signal for each sub-field period, and given to the light valve, thereby causing the light valve to output pulse-width modulated light according to the luminance signal for each sub-field period.
According to the ninth aspect, further to the seventh aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, and a light intensity modulation circuit, supplied with the frame synchronizing signal and the sub-field synchronizing signal, for generating, based on these signals, an intensity modulating signal for each the sub-field period and outputting the intensity modulating signal to the power supply, thereby causing the light source to output light having predetermined intensity for each sub-field period. Further, the ON/OFF control means includes a light valve supplied with the light from the light source, a sub-field drive circuit, supplied with the luminance signal for each the frame period, the frame synchronizing signal, and the clock signal, for generating, based on these signals, the sub-field synchronizing signal and the luminance signal for each sub-field period, and a pulse-number modulating circuit, supplied with the sub-field synchronizing signal and the luminance signal for each the sub-field period, for generating, based on these signals, a pulse-number modulating signal and outputting the pulse-number modulating signal to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal for each sub-field period.
In the above ninth aspect, the sub-field synchronizing signal and the luminance signal for each sub-field period is generated based on the luminance signal for each frame period, the frame synchronizing signal, and the clock signal. Then, the intensity modulating signal for each sub-field period is generated based on the frame synchronizing signal and the sub-field synchronizing signal, and outputted to the power supply, causing the light source to output the light having predetermined intensity for each sub-field period. On the other hand, the pulse-number modulating signal is generated based on the sub-field synchronizing signal and the luminance signal for each sub-field period, and outputted to the light valve, thereby causing the light valve to output light modulated in the number of pulses according to the luminance signal for each sub-field period.
According to the tenth aspect, further to the seventh aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, a light intensity modulator for intensity-modulating light outputted from the light source, and a light intensity modulator drive circuit, supplied with the frame synchronizing signal and the sub-field synchronizing signal, for generating, based on these signals, an intensity modulating signal for each sub-field period and outputting the intensity modulating signal to the light intensity modulator, thereby causing the light intensity modulator to output light having predetermined intensity for each sub-field period. Further, the ON/OFF control means includes a light valve supplied with light from the light intensity modulator, a sub-field drive circuit, supplied with the luminance signal for each the frame period, the frame synchronizing signal, and the clock signal, for generating, based on these signals, the sub-field synchronizing signal and the luminance signal for each sub-field period, and a pulse-width modulation circuit, supplied with the sub-field synchronizing signal and the luminance signal for each the sub-field period, for generating, based on these signals, a pulse-width modulating signal and outputting the pulse-width modulating signal to the light valve, thereby causing the light valve to output pulse-width modulated light according to the luminance signal for each sub-field period.
In the above tenth aspect, the sub-field synchronizing signal and the luminance signal for each sub-field period are generated based on the luminance signal for each frame period, the frame synchronizing signal, and the clock signal. Then, the intensity modulating signal for each sub-field period is generated based on the frame synchronizing signal and the sub-field synchronizing signal, and is outputted to the light intensity modulator, thereby causing the light intensity modulator to output light having predetermined intensity for each sub-field period. On the other hand, the pulse-width modulating signal is generated based on the sub-field synchronizing signal and the luminance signal for each sub-field period, and is outputted to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal for each sub-field period.
According to the eleventh aspect, further to the seventh aspect, the light-emitting means includes a light source, a power supply for supplying predetermined electric power to the light source, a light intensity modulator for intensity-modulating light outputted from the light source, and a light intensity modulator drive circuit, supplied with the frame synchronizing signal and the sub-field synchronizing signal, for generating, based on these signals, an intensity modulating signal for each sub-field period and outputting the intensity modulating signal to the light intensity modulator, thereby causing the light intensity modulator to output light having predetermined intensity for each sub-field period. Further, the ON/OFF control means includes a light valve supplied with light from the light intensity modulator, a sub-field drive circuit, supplied with the luminance signal for each the frame period, the frame synchronizing signal, and the clock signal, for generating, based on these signals, the sub-field synchronizing signals and the luminance signal for each the sub-field period, and a pulse-number modulation circuit, supplied with the sub-field synchronizing signal and the luminance signal for each the sub-field period, for generating, based on these signals, a pulse-number modulating signal and outputting the pulse-number modulating signal to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal for each sub-field period.
In the above eleventh aspect, the sub-field synchronizing signal and the luminance signal for each sub-field period are generated based on the luminance signal for each frame period, the frame synchronizing signal, and the clock signal. Then, the intensity modulating signal for each sub-field period is generated based on the frame synchronizing signal and the sub-field synchronizing signal, and outputted to the light intensity modulator, thereby the light intensity modulator outputs light having predetermined intensity for each sub-field period. On the other hand, the pulse-number modulating signal is generated based on the sub-field synchronizing signal and the luminance signal for each sub-field period, and is outputted to the light valve, thereby causing the light valve to output pulse-number modulated light according to the luminance signal for each sub-field period.